It has been conventional to effect recharging of motive power batteries by controlling the charge time through a motor-driven timer. In one use of such a timer, the duration of the charging cycle has been caused to be equal to the time set on the timer by the user.
Numerous different types of batteries are known. For example those typically used in trucks are either a low-maintenance type battery or a conventional type battery with antimonial grids. Conventional battery chargers have different manual settings for different types of batteries and typically battery chargers are usually dedicated to a certain type battery. There has been a need for an automatic battery charger which can distinguish between different types of batteries so that a user will not mistakenly apply a wrong charging level and time to a battery. Until the present invention the prior art method of accurately charging batteries required the installation of expensive and fragile ampere-hour integrators on trucks in order to determine the depth of discharge of the battery. Few trucks are equipped with ampere-hour integrators and therefore the only other way of determining the depth of discharge is to estimate it from a measurement of the specific gravity of electrolyte. This method is not accurate because the depth of discharge for a specific gravity is not a constant for all batteries, and is also temperature dependent.
Once the depth of discharge has been determined, the battery charger timer must be set so that the charging cycle will be terminated when the battery is fully charged. The setting is based on depth of discharge, type of battery, temperature, age and condition of battery.
The last step is to set the battery charger output voltage and current control to charge either a low counter-voltage battery or a high counter-voltage battery. Typically conventional batteries have a low counter-voltage, and low maintenance batteries have a high counter-voltage.
The technical expertise required to make the necessary measurements and decisions is not always available to the majority of battery users. Therefore, typical industrial truck battery chargers are designed to overcharge the battery to make certain it always receives a least a full charge. The overcharge reduces battery life, increases water loss in the electrolyte and wastes electrical energy.
One battery charger control circuit for use in automatic battery chargers is illustrated in U.S. Pat. No. 4,131,841, which discloses an improved battery charger having a current limiting transformer for supplying a charging current. The transformer includes primary and secondary coils wound about a core and has a shunt path for a portion of the magnetic flux induced by the voltage appearing on the primary. A pair of silicon controlled rectifiers are alternately triggered into their forward conductive states at points relatively early in each alternating current half cycle to provide a maximum charging current when a substantially discharged battery is to be recharged. As the charging process progresses, the battery voltage increases and at a predetermined value of the battery voltage a smooth transition from the current-controlled mode to a voltage-controlled mode has been completed, the SCRs are triggered into conduction much later in each cycle, thereby furnishing a very low or trickle current which can be continued indefinitely without damage to the battery. Simple adjustments are provided for determining the maximum voltage at which the changeover is to begin.
U.S. Pat. No. 4,233,553 discloses an automatic dual mode battery charger wherein a voltage regulating means provides two modes of operation. A current detector connected in series with the voltage regulator and the battery provides a means for detecting current flow through the battery and controls the operation of the voltage controller, to change the output of the voltage regulating means between the two modes of operation.
U.S. Pat. No. 4,217,533 relates to a device for charging batteries wherein the device provides a substantially constant charging current for a first charging interval until a voltage level which is less than that of a fully charged battery is reached. At this time, the device continues charging in a sequence of subsequent time intervals with charging currents which decrease at different rates in each interval until the battery is fully charged. The duration of each of the subsequent time intervals and the rates at which the charging currents decrease may be adjusted to shorten charging time while minimizing gasification of water in the battery.
U.S. Pat. No. 3,979,658 disclose an automatic electric battery charging apparatus of the taper type having means for comparing a reference signal with a control signal varying with battery voltage, and terminating the charge when the rate of rise of battery voltage falls below a predetermined value. To prevent spurious operation due to mains voltage variation, the control signal comprises the difference between a signal dependent on battery voltage and a signal dependent of a.c. supply voltage.
U.S. Pat. No. 4,313,078 relates to a battery charging system in which the ampere-hour discharge of the battery is sensed for controlling the battery charging rate. The battery is charged at a relatively high charge rate during a first time period proportional to the extent of battery discharge and at a second lower rate thereafter.